A desirable characteristic of some high voltage devices, such as x-ray sources, especially portable x-ray sources, is small size. An x-ray source is comprised of an x-ray tube and a power supply. Transformers and a high voltage sensing resistor in the power supply can significantly cause the power supply to be larger than desirable.
An x-ray source can have a high voltage sensing resistor used in a circuit for sensing the tube voltage. The high voltage sensing resistor, due to a very high voltage across the x-ray tube, such as around 10 to 200 kilovolts, can have a very high required resistance, such as around 10 mega ohms to 100 giga ohms. The high voltage sensing resistor can be a surface mount resistor and the surface of the substrate that holds the resistor material can have surface dimensions of around 12 mm by 50 mm in some power supplies. Especially in miniature and portable x-ray tubes, the size of this resistor can be an undesirable limiting factor in reduction of size of a power supply for these x-ray tubes.
X-ray tubes can have a transformer (“filament transformer”) for transferring an alternating current signal from an alternating current (AC) source at low bias voltage to an x-ray tube electron emitter, such as a filament, at a very high direct current (DC) voltage, or bias voltage, such as around 10 to 200 kilovolts. A hot filament, caused by the alternating current, and the high bias voltage of the filament, relative to an x-ray tube anode, results in electrons leaving the filament and propelled to the anode. U.S. Pat. No. 7,839,254, incorporated herein by reference, describes one type of filament transformer.
X-ray tubes can also have a transformer (called a “high voltage transformer” or “HV transformer” herein) for stepping up low voltage AC, such as around 10 volts, to higher voltage AC, such as above 1 kilovolt. This higher voltage AC can be used in a high voltage generator, such as a Cockcroft-Walton multiplier, to generate the very high bias voltage, such as around 10 to 200 kilovolts, of the x-ray tube filament or cathode with respect to the anode. The size of both the high voltage transformer and the filament transformer can be a limiting factor in reduction of the size of the x-ray source.